Graphene, a monolayer of carbon atoms packed into a two dimensional
(2D) honeycomb lattice, has attached a great amount of attention
from both experimental and theoretical points of view [1]}
since it was isolated and demonstrated to be stable
[2]}, [3]}. It is a basic building block for graphite
materials of all other dimensionalities, e.g., it can be wrapped up
into 0D fullerenes, rolled into 1D nanotubes, or stacked into 3D
graphite. Due to its unique electronic properties, i.e., its
conduction electrons behave as massless Dirac fermions
[3]}, [5]}, a lot of interesting phenomena such as the
finite conductance at zero concentration [3]}, the unusual
half integer quantum Hall effect [5]}, and the Klein
tunneling [8]} have been observed in the graphene and
theoretically discussed in the framework of the massless fermion
Dirac's model [3]}, [10]}.
